This talk focuses on the research conducted in recent years and discusses how U. mutabilis has developed into a model organism with the specific perspective that a reductionist model system allows. The field of systems biology will achieve a comprehensive, quantitative understanding of the dynamic interactions between Ulva and its associated bacteria to better predict the behaviour of the system. For instance, gardening the microbiome in aquaculture reduces the operational taxonomic units in cultivated compared to freshly isolated Ulva with its native microbiome. U. mutabilis, which is conspecific with the cosmopolitan Ulva compressa, also serves as a unique model system to investigate the requirements for withstanding environmental stresses, such as cold temperatures or micropollutants.